Air Quality in Barns Critical for Horse and Human Health

Most equestrians know firsthand the dangers that accompany their passion for horses: bumps and bruises (and the occasional broken bone) are nothing out of the ordinary. But fewer horse owners are aware of the damage they can receive by simply spending time in the barn; poor air quality can be just as dangerous for owners as it is for the horses in their care.

"We care about the airway quality in barns because of its effect on both horses and humans," noted Melissa Mazan, DVM, Dipl. ACVIM, associate professor and director of the equine sports medicine program at Tufts Cummings School of Veterinary Medicine's Hospital for Large Animals in North Grafton, Mass. Mazan presented on the topic at the 2011 America College of Veterinary Internal Medicine Forum, held June 15-18 in Denver, Colo.

Unlike in the swine and poultry industries, she explained, air quality in horse barns is not subject to regulations and lacks oversight from the Occupational Health and Safety Administration. Mazan said that up to 80% of stabled horses develop airway inflammation, and this statistic likely has consequences for humans working in barns as well: They are subjected to the same environmental conditions as their equine charges.

Responses to a widespread questionnaire sent to horse barn employees revealed that nasal and throat irritation were common complaints from workers, as were chest issues including breathing difficulty, wheezing, productive cough, and shortness of breath.

Mazan explained that the main causes of airway dysfunction in both people and horses are related to exposure to airborne particles including:

Endotoxins (the cell wall of Gram-negative bacteria released in horse manure) in particle dust.

Irritating particles come in different sizes, ranging from coarse (10 microns) to fine (about two and a half microns); for perspective, the thickness of a human hair is 60 microns. Particles less than 4 microns are "respirable" (i.e., they can be breathed in), potentially settling in the smallest portions of the lungs called the alveoli. Nasal hairs and sneezing typically filter the five to 10 micron particles, but if any of those do travel to the upper airways and trachea, nasal and throat irritation generally occur.

Particles up to 30 microns that aren't cleared by coughing and the mucociliary escalator (small fibers that "beat" in a coordinated manner to move the thin layer of mucus that floats on top of the cilia and the debris stuck to it out of the lungs and up the trachea, where the horse swallow it) can settle in lower airways, also causing irritation. Particles smaller than one micron can even account for human cardiovascular disease due to dissolution or uptake in the bloodstream.

Mazan suggested that air quality testing is a good way to identify the presence of a problem and localize the source within a barn, making it easier to reduce the risk of respiratory problems in horses and humans. Many commercial testing devices effectively capture particulates and/or volatile gases, such as ammonia, for analysis.

Respiratory disease in humans is caused by 0.43 mg/m3 (milligrams of respirable irritants per cubic meter of air), with 0.16 mg/m3 causing a decline in lung function over eight hours; the statistics were similar in horses, Mazan noted. She added that horse barns typically test at 0.52-4.16 mg/m3 of respirable dust.

Normal hay can generate 19.3 mg/m3 respirable dust in a horse's breathing zone whereas dusty hay can create up to 81 mg/m3, Mazan noted. These numbers increase significantly when a barn is closed up in winter, she added.

Arena dust is another culprit in circulating small particles of heavy metals as is road traffic adjacent to the stable. Endotoxins also have deleterious effects on airway function, particularly when inhaled in combination with other noxious particulates.

Regarding bedding options, Mazan explained that while straw has a higher particulate count than shavings, what is most notable is that forage (hay) is more important in determining what horses actually breathe in; she reported that horses living outdoors are exposed to negligible amounts of particulates even when fed the same hay as stabled horses.

Mazan suggested that when possible, house and work with horses outdoors, as the risk factors for airway diseases are reduced outside barn walls. Additionally, ensure your barn has proper ventilation and air movement, as these factors can also reduce the risk of developing airway diseases.

About the Author

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado,
and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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